Not applicable.
The present invention relates generally to sealed bearing earth boring drill bits, such as rotary cone rock bits. More particularly, the invention relates to drill bits that have a dual seal arrangement for protecting internal bearing elements. Yet more particularly, the present invention relates to providing for pressure communication between the interior and exterior of earth boring dual-seal drill bits.
During earthen drilling operations with the use of sealed bearing drill bits, such as rotary cone drill bits, it is necessary to protect the bearing elements of the bit from contamination in order to sustain bit operability. In particular, it is desirable to isolate and protect the bearing elements of the bit, such as bearings, bearing lubricant and bearing surfaces that are located in a bearing cavity or cavities between each corresponding bit leg and roller cone, from earthen cuttings, mud and other debris in the drilling environment. Introduction into the bearing system of such contaminants can lead to deterioration of the bearing lubricant, bearings and bearing surfaces, causing premature bit failure. It is well known in the art to provide an annular seal around the bearing elements to prevent contamination thereof by particles entering through the annular opening and into the gap that is formed between each leg and corresponding roller cone and that extends to the bearing cavity.
In a downhole drilling environment, the borehole contains xe2x80x9cdrilling fluid,xe2x80x9d which can be drilling mud, other liquids, air, other gases, or a mixture or combination thereof. In the typical liquid drilling environment of a petroleum well, the downhole fluid pressure at the location of the drill bit, the xe2x80x9cexternal pressure,xe2x80x9d can be very high and fluctuating. At the same time, internal pressure within the bearing cavity, the xe2x80x9cinternal pressure,xe2x80x9d can also be very high and fluctuating due, for example, to thermal expansion and out-gassing of lubricant in the bearing cavity, and cone movement relative to the leg. These high pressure changes internal and external to the bearing cavity may cause a differential pressure across the bearing seal, thus resulting in a major load on the seal. When the internal pressure is greater than the external pressure, the seal may be drawn to and possibly extruded into the gap. Likewise, a greater external pressure can cause the seal to be drawn in the direction of the bearing cavity and possibly extruded therein. This may cause excessive wear to the seal and eventual bit inoperability. Furthermore, when the pressure differential reaches a certain level in each above scenario, the seal can leak, allowing lubricant to pass from the bearing cavity into the gap in the first scenario, and drilling fluid to pass from the gap into the bearing cavity in the second scenario.
Generally, when the internal pressure and the external pressure are equal, the differential pressure across the bearing cavity seal will be zero. There will be no pressure to force the drilling fluid or lubricant by the seal, or to force the seal into the gap or bearing cavity. Thus, it is generally desirable to achieve or maintain a differential pressure of approximately zero. In the prior art, a lubricant reservoir system having a flexible diaphragm located in a lubricant reservoir cavity in the bit leg is used to equalize the internal and external pressure. The flexible diaphragm separates the internal lubricant from the external drilling fluid and communicates the external pressure to the portion of the bearing seal adjacent to the bearing cavity. This type of pressure compensation system for a single seal bit is schematically shown in FIG. 1a. 
Referring to FIG. 1a, when the external, or borehole, pressure Pd of the drilling fluid in the borehole B, increases and is greater than the internal pressure Pg in the bearing cavity, the seal S1 will be forced inwardly toward the bearing cavity B2. With the use of a flexible diaphragm D1 the external pressure Pd is also applied to the diaphragm D1, which transmits the pressure Pd, equalizing it with the internal pressure Pg. As a result, the pressure on both sides of the seal S1 is balanced, preventing the occurrence of any differential pressure across the seal S1. Similarly, when the pressure Pg increases, Pg will temporarily be larger than Pd, causing the diaphragm D1 to expand outwardly to increase the internal volume of the bearing cavity B2. As the internal volume increases, the internal pressure Pg will decrease. Pg will drop to equilibrium with Pd, and the internal volume will stop increasing.
Dual seal arrangements have been proposed having an outer seal around a primary inner seal. The purpose of including a second seal is typically to provide a second layer of protection from particles entering the gap through the annular opening. When an outer seal is added, it may be necessary, such as in drill bits used for petroleum wells, that the bit be capable of compensating for the differential pressure across both seals. FIG. 1b shows a two-seal schematic with both seals providing substantially absolute seals, the xe2x80x9cspacexe2x80x9d Sp formed between the seals S1, S2 being completely filled with incompressible fluid, and there being no variation in the density of the incompressible fluid. In this scenario, the incompressible fluid in space Sp between the seals S1, S2 acts like a rigid body that transmits pressure from Pg1, which is the (internal) bearing cavity pressure, to Pd and from Pd to Pg1. For example, when the external fluid pressure Pd increases, diaphragm D1 will be pushed inwardly, causing the internal pressure Pg1 to equal the external pressure Pd. Because the fluid between seals S1 and S2 is incompressible, it will transmit the increased pressure between S1 and S2 and neither seal S1 or S2 will be displaced.
However, during borehole drilling operations, such as with rotary cone sealed bearing drill bits, various factors will alter ideal conditions and require something more to equalize the differential pressure across both seals S1 and S2. For example, there is relative movement between the roller cone and bit leg, which causes the volume of the space Sp between the seals S1 and S2 to significantly increase and decrease. A change in the volume of the space Sp will change the chamber pressure Pg2 in the space Sp, causing conditions where Pg2 greater than Pd, Pg1 upon contraction of the space Sp, and where Pg2 less than Pd, Pg1 upon expansion of the space Sp. Thus, there will be differential pressures across both seals S1, S2, causing their movement and possible extrusion, which can cause accelerated seal wear and eventual bit failure.
Another potential factor altering ideal conditions is the thermal expansion, or out-gassing, of the incompressible fluid between the seals S1, S2 due to elevated temperatures within the bit. Referring to FIG. 1b, expansion of the incompressible fluid in the space Sp between the seals S1, S2 will elevate the chamber pressure Pg2. Increasing the chamber pressure Pg2 can cause a differential pressure across the seals S1, S2 such that Pg2 greater than Pd, Pg1, which can result in accelerated wear and possible extrusion of seals S1, S2. Still another factor is the existence of air trapped in the space Sp between the seals S1, S2. In this instance, the mixture of air and fluid in space Sp is not incompressible. When external pressure Pd increases, Pg1 will eventually equal Pd due to the diaphragm D1, but Pd  greater than Pg2 and Pg1 greater than Pg2 because of the presence of air in the space Sp between the seals S1, S2. The chamber pressure Pg2 in the space Sp will not increase until the seals S1, S2 move closer together and the air volume in space Sp decreases. This differential pressure across seals S1, S2 will cause the movement and possible extrusion of the seals into the space Sp and excessive wear on the seals.
In the prior art, U.S. Pat. No. 5,441,120, which is hereby incorporated by reference herein in its entirety, discloses the use of an additional flexible diaphragm D2, such as shown in FIG. 1c herein, to attempt to equalize, or balance the chamber pressure Pg2 of the space Sp with the external pressure Pd or internal pressure Pg1. Further increases in external pressure Pd will thereafter be transmitted through the fluid in the space Sp. Such a system has various disadvantages. For example, a system made in accordance with U.S. Pat. No. 5,441,120 requires or occupies much space within the bit leg, structurally weakening the bit. For another example, such a system does not allow for pressure relief from the space Sp, such as caused by thermal expansion and outgassing of the incompressible fluid between the seals S1, S2, which can cause damage to the seals as described above. It should be understood that there are other disadvantages and features of the disclosure of U.S. Pat. No. 5,441,120 as well as various features of the invention of each claim herein that distinguish one from the other. Thus, in any comparison, the disclosure of U.S. Pat. No. 5,441,120 should be compared as a whole to the claimed invention of any particular claim herein as a whole to distinguish them.
U.S. Pat. Nos. 4,981,182 and 5,027,911, which are also hereby incorporated herein in their entireties, disclose various embodiments of drill bits including inner and outer seals and where lubricant is bled out of the bit past the outer seal to prevent drilling debris from accumulating and damaging the inner and outer seals. In some such embodiments, passages in the bit allow lubricant to travel from the bearing cavity to the space between the seals. In other embodiments, a hydrodynamic inner seal is used, which allows the leakage of lubricant from the bearing cavity to the space between the seals. In both instances, the pressure of the lubricant presumably forces the outer seal to open and allow the bleeding of lubricant from the bit. These systems also have various disadvantages. For example, the continuous bleeding of lubricant past the outer seal (particularly if the outer seal fails) can lead to the depletion of bearing lubricant in the bit, and cause bearing and bit damage due to a lack of lubricant. For another example, if the space between the seals in such configurations is not filled with lubricant, such as which will occur if there is a decrease or stoppage in the flow of lubricant from the bearing cavity to the space, a high pressure differential across the seals can result, causing damage to the seals as described above. For yet another example, with many such embodiments, because the space between the seals and the bearing cavity are in fluid communication, there exists the possibility that debris or drilling fluid bypassing the outer seal, such as when the outer seal fails, will move through the space between the seals and into the bearing cavity, causing contamination and damage to therein and to the bearing elements. It should be understood that there are other disadvantages and features of the disclosures of U.S. Pat. Nos. 4,981,182 and 5,027,911 as well as various features of the invention of each claim herein that distinguish them. Thus, in any comparison of U.S. Pat. No. 4,981,182 or 5,027,911 and any claim herein, such disclosure should be compared as a whole to the claim as a whole to distinguish them.
Thus, there remains a need for improved techniques and mechanisms for substantially balancing or minimizing the pressure differential upon the primary and secondary seals of a dual seal configuration, particularly by allowing pressure communication between the interior and exterior of the drill bit. Ideally, the devices and techniques will accommodate cone movement, thermal expansion of the fluid and/or out-gassing between the primary and secondary seals, and trapped air in the space between the seals. Especially well received would be pressure communication devices that do not require substantial additional components, large space requirements in the bit, or highly complex manufacturing requirements for the bit. Also well received would be a pressure communication technique and device that will prevent the pressure differential across the dual seals from exceeding an upper limit, such as, for example, 100 psi. It would also be advantageous to include the use of an incompressible fluid having the capabilities of retaining sufficient viscosity to act as a medium for the transmission of energy between the primary and secondary seals, of retaining its lubrication properties, and/or of slowing the intrusion of abrasive particles to the primary sealxe2x80x94when and after the incompressible fluid is exposed to drilling fluid. These and other needs in the art will become apparent to those of skill in the art upon review of this patent specification, claims and drawings.
In accordance with the present invention, there is provided techniques, methods and apparatuses for communicating fluid pressure between a borehole and the space between the seals of a dual-seal drill bit. The invention includes a drill bit for use in a borehole at least partially containing drilling fluid, including a bit body having at least two bit components, the bit components including at least one leg, the leg having a journal segment, the bit components further including a roller cone rotatably mounted upon the journal segment and forming at least one bearing cavity therebetween. The drill bit also includes an annular primary seal disposed between the leg and the roller cone and an annular secondary seal disposed between the leg and the roller cone and between the annular primary seal and the borehole. The annular secondary seal may be primarily elastomeric, may be primarily axially or radially energized, and/or may be disposed in an annular groove formed in one of the bit components or an annular interstice formed between the leg and the roller cone.
An annular space is disposed between the annular primary seal and the annular secondary seal. The annular space may at least partially contain fluid and may be in substantially absolute fluid isolation from the bearing cavity. The annular space may at least partially include a grease possessing a water washout value of under approximately 50% per ASTM D-4049 water spray test for lubrication characteristics, the grease including a polymer tackifier of between approximately 1% and approximately 5% by weight.
In one aspect of the invention, there is include means for permitting the flow 6f fluid from the annular space to the borehole. The drill bit can be configured such that the means further permits the flow of fluid from the borehole to the annular space. The means can be integral with the annular secondary seal, integral with at least one of the bit components or a combination thereof.
In another aspect of the invention, a first contact pressure occurs at the primarily dynamic sealing surface of the annular primary seal and a second contact pressure occurs at the primarily dynamic sealing surface of the annular secondary seal, the first contact pressure being greater than the second contact pressure. In yet another aspect of the invention, the annular secondary seal includes a primarily dynamic sealing surface and a primarily static sealing surface, wherein a first contact pressure occurs at the primarily dynamic sealing surface and a second contact pressure occurs at the primarily static sealing surface, the first contact pressure and the second contact pressure being unequal. In still another aspect of the invention, the annular secondary seal includes a sealing surface engageable with one of the bit components, wherein the sealing surface includes first and second regions. A first contact pressure occurs at the first region of the sealing surface and a second contact pressure occurs at the second region of the sealing surface, the first contact pressure being greater than the second contact pressure.
In accordance with another aspect of the invention, the annular space has a chamber pressure which may be altered by allowing the passage of fluid from the annular space to the borehole and from the borehole to the annular space. In a variation of this aspect, when a differential pressure occurs between the chamber pressure and the borehole pressure, the chamber pressure may be altered when the differential pressure is between approximately 0 psi and approximately 100 psi; and, in another variation, between approximately 30 psi and approximately 70 psi.
In another aspect of the invention, the bit may be designed so that fluid migrates from the annular space to the borehole when the chamber pressure is greater than the borehole pressure. The bit may be further designed so that fluid migrates from the borehole to the annular space when the borehole pressure is greater than the chamber pressure. In another aspect, the annular secondary seal includes first and second side surfaces adjacent to the sealing surface, and at least one of the bit components includes at least one non-energizing surface at least partially engageable with one of the first and second side surfaces of the annular secondary seal. The non-energizing surface of the bit component includes first and second regions, the first region of the non-energizing surface being uneven with respect to the second region of the non-energizing surface. Further, the first region of the non-energizing surface may include at least one surface feature.
In still another aspect of the invention, the annular secondary has a sealing surface engageable with at least one bit component, the sealing surface having first and second adjacent regions, wherein the thickness of the annular secondary seal at the first region of the sealing surface is greater than the thickness of the annular secondary seal at the second region of the sealing surface. In yet another aspect, the annular secondary seal includes at least one region having a tapered cross-section, or the cross-section of the entire annular secondary seal is tapered. Still, a further aspect of the invention includes an annular secondary seal including at least one region having an at least partially non-symmetrical cross-section.
In another aspect, the annular secondary seal including at least first and second circumferentially adjacent regions, a primarily static sealing surface and a primarily dynamic sealing surface. Each of the first and second circumferentially adjacent regions has a height measured between the primarily static and primarily dynamic sealing surfaces. Further, at least one of the static and dynamic sealing surfaces is at least partially disposed on the first and second circumferentially adjacent regions, the height of the first circumferentially adjacent region being greater than the height of the second circumferentially adjacent region.
In another aspect, at least one of the bit components includes an annular groove having first and second circumferentially adjacent regions, wherein the width of the first circumferentially adjacent region is greater than the width of the second circumferentially adjacent region and the annular secondary seal is disposed within the annular groove. In still another aspect, the bit components include first and second primarily non-energizing seal engagement surfaces and the annular secondary seal has first and second sides engageable with the first and second primarily non-energizing seal engagement surfaces of the bit components, respectively. At least one of the first and second primarily non-energizing seal engagement surfaces of the bit components includes first and second regions, the first region including at least one cut-out.
In accordance with one aspect of the present invention, the bit components include first and second primarily non-energizing seal engagement surfaces and the annular secondary seal having first and second sides engageable with the first and second primarily non-energizing seal engagement surfaces of the bit components, respectively. At least one of the first and second primarily non-energizing seal engagement surfaces of the bit components includes first and second regions, the first region being uneven with respect to the second region.
In another aspect, at least one of the bit components includes an annular groove and the annular secondary seal has first and second sides and being disposed within the annular groove. The annular groove includes a first primarily non-energizing surface engageable with the first side of the annular secondary seal and a second primarily non-energizing surface engageable with the second side of the annular secondary seal, the first primarily non-energizing surface disposed between the second primarily non-energizing surface and the bearing cavity. Further, the second primarily non-energizing surface includes at least first and second circumferentially adjacent regions, the first region of the second primarily non-energizing surface including at least one cut-out, whereby the distance from the first region of the second primarily non-energizing surface to the first primarily non-energizing surface is greater than the distance from the second region of the second primarily non-energizing surface to the first primarily non-energizing surface.
In still a further aspect of the invention, the annular secondary seal includes first and second circumferentially adjacent regions and a sealing surface extending at least partially upon the first and second circumferentially adjacent regions, wherein the sealing surface of the first circumferentially adjacent region is uneven with respect to the sealing surface of the second circumferentially adjacent region.
In still a further aspect, the leg and roller cone each include at least one component surface engageable with the annular secondary seal, at least one such component surface including first and second adjacent regions, wherein the first region of the component surface is uneven with respect to the second region of the component surface. In still another aspect, at least one of the bit components includes an annular groove having at least first and second circumferentially adjacent regions, the depth of the first circumferentially adjacent region being greater than the depth of the circumferentially adjacent second region and the annular secondary seal being disposed within the annular groove. Another aspect includes an annular interstice formed between the bit components, the annular interstice having at least one seal engagement surface, the seal engagement surface having first and second circumferentially adjacent regions. The depth of the first circumferentially adjacent region of the seal engagement surface is greater than the depth of the second circumferentially adjacent region and the annular secondary seal is disposed within the annular interstice.
In accordance with another aspect of the present invention, the annular secondary seal includes a primarily dynamic sealing surface and a primarily static sealing surface, each of the primarily dynamic and static sealing surfaces engageable with one of the bit components. At least a portion of at least one of the primarily dynamic and static sealing surfaces includes a non-elastomeric porous inlay capable of at least partially allowing the passage of fluid past the annular secondary seal when the portion of at least one of the sealing surfaces is engaged with the bit component.
In still a further aspect, the drill bit has an opening in the exterior surface of the leg and a passage disposed in the leg and extending from the opening to the annular space, the passage allowing fluid communication between the annular space and the borehole. In a variation of this aspect, a plurality of passages may be disposed in the leg and extend from the opening to the annular space. The passage may be capable of allowing the flow of fluid from the annular space to the borehole and from the borehole to the annular space. A fluid control member may be disposed in the leg in fluid communication with the passage. The fluid control member may be a two-way valve, or a primarily one-way fluid valve capable of allowing the flow of fluid from the annular space to the borehole. The annular space may be filled with incompressible fluid through the passage. The annular space may be at least partially includes a grease possessing a water washout value of under approximately 50% per ASTM D-4049 water spray test for lubrication characteristics, the grease including a polymer tackifier of between approximately 1% and approximately 5% by weight.
In another aspect the annular primary seal may form a substantially absolute seal and the annular space in substantially absolute fluid isolation from the bearing cavity. An opening is disposed in the exterior surface of the leg and a passage is disposed in the leg and extending from the opening to the annular space. The passage is filled with incompressible fluid and a plug is disposed in the opening.
Another aspect of the invention involves at least one of the bit components including at least two seal engagement surfaces, the annular secondary seal including a primarily dynamic sealing surface and a primarily static sealing surface, each the sealing surface of the annular secondary seal having a width and being engageable at the width with one of the seal engagement surfaces of the bit components. At least one of the annular primarily dynamic and primarily static sealing surfaces includes first and second regions, the width of the first region being smaller than the width of the second region.
Still, a further aspect of the invention includes an incompressible fluid for use to lubricate a seal in a sealed bearing drill bit, the drill bit useful in a borehole at least partially containing drilling fluid and solid particles, including a grease capable of lubricating at least one seal after the grease contacts drilling fluid. The grease may further capable of trapping solid particles to assist in preventing the ingress of solid particles to the seal, and/or transmitting energy between first and second seals after the grease contacts drilling fluid. The grease may be disposed between a primary seal and a secondary seal. The grease may possess a water washout value of under approximately 50% per ASTM D-4049 water spray test for lubrication characteristics. 30% per ASTM D-4049 water spray test for lubrication characteristics, and/or a polymer tackifier of between approximately 1% and approximately 5% by weight. The grease may include between approximately 10 percent and approximately 30 percent by weight of at least one mineral oil and between approximately 70 percent and approximately 90 percent by weight of at least one synthetic oil, and/or between approximately 1.0 percent and approximately 10.0 percent by weight of silica thickener and between approximately 1.0 percent and approximately 5.0 percent by weight of tackifier.
Accordingly, the present inventions comprise various combinations of features and advantages which enable it to substantially advance the technology associated with dual-seal pressure communication techniques and apparatuses. Each of these aspects of the invention, which may be used alone or in a combination with others, provides an improved technique and mechanism for substantially balancing or minimizing the pressure differential upon the primary and secondary seals of a dual seal configuration, particularly by allowing pressure communication between the interior and exterior of the drill bit. The present invention includes devices that accommodate cone movement, thermal expansion of the fluid and/or out-gassing between the primary and secondary seals, and trapped air in the space between the seals. Many of the pressure communication devices of the present invention do not require substantial additional components, large space requirements in the bit, or highly complex manufacturing requirements for the bit. Also included are various pressure communication techniques and devices that will prevent the pressure differential across the dual seals from exceeding an upper limit, such as, for example, 100 psi. Yet a further feature of many aspects of the invention involves the use of an incompressible fluid having the capabilities of retaining sufficient viscosity to act as a medium for the transmission of energy between the primary and secondary seals, of retaining its lubrication properties, and/or of slowing the intrusion of abrasive particles to the primary sealxe2x80x94when and after the incompressible fluid is exposed to drilling fluid.
The characteristics and advantages of various aspects and embodiments of the present invention described herein, as well as additional features and benefits, will be readily apparent to those skilled in the art upon reading the following detailed description, referring to the accompanying drawings and reading the appended claims.
It should be understood that each claim herein does not necessarily require or encompass more than one feature or aspect of the present invention. Further, the disadvantages of the prior art and advantages, features and aspects of the present invention should not be considered limitations to any of the appended claims unless expressly recited therein, each claim being construed independently.